Arg is a novel human gene related to c-abl and located on the long arm of the chromosome 1 (1q24-25). We have characterized the full length arg cDNA. The arg predicted coding sequence, when compared with c-abl, defines the abelson subfamily of the cytoplasmic tyrosine kinases. In particular, the tyrosine kinase domain as well as the SH2 - SH3 regions are highly similar. The homology with abl decreases in the carboxyl terminus. Of note is the finding that arg, like c-abl, is expressed as two transcripts encoding proteins that differ only in their amino termini. In order to obtain high titer antibodies specific for arg protein, segments of the arg coding sequence were expressed in an inducible bacterial system utilizing the T7 promoter. Arg coding sequences were expressed either as a fusion protein containing 14 amino acids of the phage T10 protein or 260 amino acids. The later fusion proteins are insoluble and facilitate the purification of the antigen for injection into animals. Polyclonal sera have been raised against these fusion proteins in rabbits, and the preparation of monoclonal antibodies will be attempted in mice. The arg antibodies thus produced will be used to identify the cellular arg protein as well as investigate its subcellular localization and enzymatic activity. This characterization of the arg protein will provide important information on the role of this new gene in cell growth and signal transduction.